1. Field of the Invention
This invention relates to systems for the rapid conversion of aircraft from passenger carriage to freight carriage and vice-versa.
2. Review of the Art
The high capital cost of passenger aircraft means that economic operation requires high utilization, and the ability to convert an aircraft between passenger and freight carriage can assist in improving utilization. So-called commuter aircraft present a particular problem in this regard, since the type of short range passenger traffic to which they cater is substantially a daytime traffic, leaving the aircraft unused at night. Nighttime traffic is frequently available in the form of courier and parcel traffic, but only if the aircraft can be converted between passenger and freight carriage sufficiently rapidly to enable both traffic to be carried within a single day. An alternative solution is to increase the size of the freight compartment within the aircraft at the expense of the passenger compartment, which represents a compromise and fails to exploit the capacity of the aircraft effectively for either passengers or freight, unless the relative proportions of passenger and freight space can be rapidly varied to suit demand.
When large aircraft are converted for freight carriage, provision is made for the freight to be loaded on pallets or in containers which are anchored to the aircraft structure; an exemplary arrangement is that shown in U.S. Pat. No. 3,480,239 (Jensen et al). If maximum freight storage is to be provided, it may be desirable to remove overhead baggage storage lockers, and U.S. Pat. No. 5,108,048 (Chang) discloses a system for facilitating the removal and reinstallation of such lockers.
In small aircraft, courier or parcel traffic will commonly be manually loaded rather than being palletised or containerised, and indeed such aircraft commonly have cargo doors which are neither of sufficient dimensions nor conveniently located to accept pallets or containers of any substantial size. Loose loaded packages, or packages in small bags or containers, on the other hand, both require the available cargo space to be divided by adequately anchored restraining nets, for example as shown in U.S. Pat. No. 2,669,402 (Del Mar), and also require that any internal finish of the aircraft passenger cabin that remains installed be adequately protected from damage by the cargo. It is difficult, if not impossible, to provide suitable anchorages for cargo nets to the fuselage of the aircraft through the cabin finish without impairing the appearance of the latter and giving it a makeshift appearance whilst the aircraft is functioning as a passenger carrier. Significant dismantling of the interior finish of the cabin is not practicable as part of a rapid and reversible conversion system.
U.S. Pat. No. 4,483,499 (Fronk) discloses a system for converting small passenger aircraft for the carriage of patients and cargo by the attachment of rack like structures to tracks in the aircraft normally utilized to secure its seats. Fronk is primarily concerned with providing means for converting an aircraft for air ambulance purposes, and overcoming the problem of loading stretchers through relatively small doors or hatches. Whilst his racks could be utilized for securing cargo, they are unsuitable for the storage of loose cargo of the kind presently contemplated, would provide little protection to the internal finish of the aircraft, and themselves occupy valuable cargo space.
Both the Fronk and Jensen patents make use of seat tracks provided longitudinally of the passenger cabin of the aircraft to secure their freight conversion equipment. These tracks are used to secure, releasably, passenger seating, in a manner which permits the seating of an aircraft to be rapidly removed or rearranged. Examples of such tracks, and fastenings for use with them, are shown in U.S. Pat. Nos. 5,131,606 (Nordstrom) and 5,169,091 (Beroth).